This invention relates generally to irrigation sprinklers of the impact or reaction drive types, and, more specifically, to an apparatus and method for assembling sprinklers, having plastic pivoting pins protected by integral bearing-surface shields, through an automated process.
Conventional impact drive sprinklers have been manufactured substantially of metals such as brass, and include an impact drive mechanism which pivots about a vertical axis. The drive mechanism typically comprises a counterweighted impact drive arm which is supported on and pivots about a durable stainless steel fulcrum pin, a spring which biases the arm in one rotational direction about the fulcrum pin, and a deflector spoon unit for cyclically interrupting a water stream projected from the sprinkler resulting in a reaction force driving the arm in an opposite rotational direction. Because the pin firmly positions the impact drive mechanism upon a sprinkler main body and provides the pivotal axis therefor, proper placement of the pin is crucial to the correct operation of the sprinkler.
One problem encountered with such prior sprinklers is that manufacturing costs are relatively high in view of the time-consuming and expensive manual labor required to properly assemble the various sprinkler components. More specifically, the impact drive mechanism is normally placed within a sprinkler body window defined by an inverted, generally U-shaped bridge which is integrally formed with a pair of legs extending upwardly from the main body of the sprinkler. The drive arm, the spring and any associated bearing structure must be properly aligned within this window prior to placement of the fulcrum pin for proper sprinkler operation in use. Unfortunately, the closed loop formed by the sprinkler window makes automated sprinkler assembly impracticable, and, as a result, necessitates hand alignment of the drive mechanism components therein.
In recent years, sprinkler manufacturers have produced sprinklers of the impact drive type from molded plastics in an effort to reduce manufacturing costs. Although from a cost standpoint it is generally considered desirable to provide a plastic fulcrum pin for the drive arm pivotal axis in such sprinklers, stainless steel pins are still frequently used because of their proven extended wear characteristics. It has been believed that the bearing surfaces of less expensive plastic fulcrum pins require extra protection from dirt, grit, and the like, for the pins to have adequately long lives. Consequently, when plastic fulcrum pins have been used, protective bearing-surface shields have been provided as additional components to surround any portions of the plastic pins which may be exposed to abrasives while in use.
Efforts to incorporate plastic fulcrum pins and the necessary protective bearing-surface shields into prior sprinklers ahve been frustrated primarily due to assembly difficulties. More specifically, as described in connection with conventional metal sprinklers, proper installation of the impact drive arm within the closed loop sprinkler window still requires costly hand alignment. Moreover, these installation difficulties have generally made it impossible to incorporate bearing-surface shields integrally with any other portion of the spinkler.
Accordingly, there has been a need for an apparatus and a method for assembling durable and reliable impact drive sprinklers through a substantially automated process. To this end, an improved sprinkler must eliminate the previous requirement that the impact drive mechanism be hand aligned within the sprinkler window prior to placement of the fulcrum pin. Further, when a plastic fulcrum pin is utilized, protective bearing-surface shields must be provided in an economical manner without disturbing the capability of the improved sprinkler to be assembled during an automated manufacturing process. The present invention fulfills these needs and provides other related advantages.